DENVER (CNN) -- A lawsuit filed Thursday, accusing the parents of Columbine High School student gunmen Dylan Klebold and Eric Harris of failing to supervise their children, will be expanded to other defendants, said the plaintiffs' attorney.

"This lawsuit is about duty, this lawsuit is about accountability, this lawsuit is about responsibility," said attorney Geoffrey Fieger, who filed the lawsuit in Denver on behalf of Michael and Vonda Shoels.

The Shoels' son Isaiah, an 18-year-old Columbine senior, died in the April 20 gun and bomb assault at the school.

Feiger said the suit does not mention a damage figure, but said that the parents were suing for up to $250 million.

Fieger said he intends to amend the lawsuit later to add other defendants that he believes were responsible in some way for the massacre in the Denver suburb of Littleton.

Harris, 18, and Klebold, 17, killed a dozen classmates and a teacher and wounded 23 students before they committed suicide.

"This is not about money," Fieger said. "This lawsuit is about negligence."

The suit maintains that Klebold and Harris could not have developed and executed the attack without the negligence of their parents.

"We're talking about two high school students constructing 50 bombs over a period of time, moving them into a school, having gun barrels in plain view on their dresser at the point of which the police entered Harris' home," Fieger said.

"Responsibility for violence sometimes extends beyond the person who actually pulls the trigger," Fieger said. "It sometimes extends to those who contribute to individual acts of violence."

Isaiah, who played football for another school in the area before transferring to Columbine High School, excelled at sports, his father says

Fieger noted the recent Supreme Court decision allowing a school to be held liable for failing to protect a student after school officials were repeatedly informed that the student was being sexually harassed.

When asked if he planned to sue the makers of video games with violent themes on the theory that they influenced Harris and Klebold to carry out the massacre, Fieger said he planned to consider that issue. But he added that he only pursues cases he thinks he can win.

"That (video game responsibility) is going to be a far bigger first amendment problem than the Jenny Jones case," Fieger said, referring to the talk show he successfully sued after a guest with a history of mental instability was embarrassed on the show, and later shot another guest who had described homosexual fantasies.

Fieger said he hoped to set financial precedents with the case. He blamed the insurance industry for Colorado's $250,000 limit on damages that can be awarded against non-governmental defendants. And he said it was wrong that governmental agencies such as schools could only be held liable for $150,000 in damages.

The Shoels said their legal action was not motivated by money.

"No money, no nothing, can ever bring my son back," said Michael Shoels. "This is not about money, this is about change, and that's what I'm looking for."

Should the Shoels win their case, the award money will not be donated.

"I promise you, this money will be used properly for my son and other children threatened by this organization that they say is just two kids ... which we all know is not right," Michael Shoels said, referring to the Trenchcoat Mafia, the name of a group that included Harris and Klebold.

"Three days before I buried my son, there was a guy with a long trench coat standing in my yard," Shoels added.

The Shoels said they have moved out of Jefferson County because of harassment and vandalism at their home since the shooting.

Isaiah Shoels, a popular athlete, was the only black victim of the massacre.

His parents maintain he was singled out because of his race. In interviews since the killings they have spoken out against racial hatred and urged parents to take more responsibility for their children.

There was no immediate comment on the lawsuit from the gunmen's parents, Wayne and Katherine Harris and Thomas and Susan Klebold.